Spring loaded relief valves are well known in the art. While such valves are generally reliable and fail-safe in nature, it is not convenient to provide such valves with external means to open the valve in order to exercise and/or test the valve. While an air or other form of pressure-biased valve can be readily provided with external actuating means, such a valve will not remain operational as a relief valve in the event of a loss of biasing pressure.
Because of the inherent problems associated with the prior art relief valves, it has become desirable to develop a valve which is operable as a relief valve independent of pressure or other external biasing forces, which is fail-safe, and which can be opened by external means for exercising and testing the valve.